Motor-driven compressor

ABSTRACT

A motor-driven compressor includes a compression mechanism, an electric motor, a housing, a drive circuit unit, a cover body, and a shield. The compression mechanism has a compression chamber and compresses refrigerant. The electric motor drives the compression mechanism. The housing accommodates the compression mechanism and the electric motor. The drive circuit unit drives the electric motor. The drive circuit unit includes a multi-layer board and electronic components mounted on the multi-layer board. The multi-layer board includes a ground layer. The cover body covers the drive circuit unit. The cover body is arranged at an outer side of the housing. The shield encompasses at least some of the electronic components. The shield is electrically connected to the ground layer of the multi-layer board.

TECHNICAL FIELD

The present invention relates to a motor-driven compressor including an electric motor that drives a compression mechanism.

BACKGROUND ART

Japanese Laid-Open Patent Publication No. 2011-247215 discloses an example of a motor-driven compressor. The motor-driven compressor includes a compression mechanism, which draws in refrigerant and compresses the refrigerant, an electric motor, which drives the compression mechanism, a housing, which accommodates the compression mechanism and the motor, and a drive circuit unit, which drives the motor. The drive circuit unit includes a circuit board formed by a multi-layer board. Electronic components such as power elements are arranged on the circuit board.

In the above motor-driven compressor, when current fluctuation occurs in an electronic component of the drive circuit unit, the electronic component generates noise that leaks from the drive circuit unit. For example, when a vehicle air conditioner is activated, noise radiated from an electronic component of the motor-driven compressor interferes with the signals received by an on-vehicle radio and affects the output of the radio. In particular, electronic components such as a transformer and a capacitor that have coils generate stronger noise than other electronic components and greatly affect peripheral devices.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a motor-driven compressor in which the noise that leaks to the surroundings of electronic components of a drive circuit unit is reduced.

One aspect of the present invention is a motor-driven compressor including a compression mechanism, an electric motor, a housing, a drive circuit unit, a cover body, and a shield. The compression mechanism has a compression chamber and compresses refrigerant. The electric motor drives the compression mechanism. The housing accommodates the compression mechanism and the electric motor. The drive circuit unit drives the electric motor. The drive circuit unit includes a multi-layer board and electronic components mounted on the multi-layer board. The multi-layer board includes a ground layer. The cover body covers the drive circuit unit. The cover body is arranged at an outer side of the housing. The shield encompasses at least some of the electronic components. The shield is electrically connected to the ground layer of the multi-layer board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a motor-driven compressor according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main section of the motor-driven compressor shown in FIG. 1.

FIG. 2A is an enlarged view of the encircled portion shown in FIG. 2.

FIG. 3 is a cross-sectional view showing a main section of a motor-driven compressor according to a second embodiment of the present invention.

FIG. 3A is an enlarged view of the encircled portion shown in FIG. 3.

FIG. 4 is a cross-sectional view showing a main section of a motor-driven compressor according to a third embodiment of the present invention.

FIG. 4A is an enlarged view of the encircled portion shown in FIG. 4.

FIG. 5 is a cross-sectional view showing a main section of a motor-driven compressor according to a fourth embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a main section of a motor-driven compressor according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of a motor-driven compressor will now be described with reference to the drawings. The first embodiment of the motor-driven compressor is an on-vehicle motor-driven compressor installed in a hybrid vehicle that travels by drive sources including an electric motor and an internal combustion engine. The motor-driven compressor forms part of a refrigerant circuit in a vehicle air conditioner. The vehicle air conditioner includes an electric motor, a condenser (not shown), a receiver (not shown), a cooling unit (not shown) including an expansion valve and an evaporator, and pipes (not shown) that connect these devices.

FIG. 1 shows a motor-driven compressor that includes a compression mechanism 11, which compresses refrigerant that serves as fluid, and an electric motor 12, which is used by the compressor to drive the compression mechanism 11. The compression mechanism 11 and the electric motor 12 are integrated in the motor-driven compressor. The motor-driven compressor includes a metal housing 13, which is formed from an aluminum metal material in the first embodiment.

The housing 13 includes a first housing body 14 and a second housing body 15. An end surface of the first housing body 14 is joined with an end surface of the second housing body 15. Bolts 16 integrally fix the first housing body 14 and the second housing body 15. The first housing body 14 includes a cylindrical portion 17 and an end wall 18, which is formed integrally with the cylindrical portion 17 to close one end of the cylindrical portion 17. In other words, the first housing body 14 is cylindrical and has a closed end. The motor-driven compressor of the first embodiment is transversely mounted in an engine compartment.

The compression mechanism 11 and the electric motor 12 are accommodated in the first housing body 14. In the cylindrical portion 17, a suction port 19 is located near the end wall 18. The suction port 19 is connected to an external refrigerant circuit (not shown), which is in communication with the inner side of the first housing body 14. During a compression operation of the motor-driven compressor, low-pressure refrigerant from the external refrigerant circuit flows through the suction port 19 into the first housing body 14.

A discharge chamber 20, which is in communication with the compression mechanism 11, is defined in the second housing body 15. The upper side of the second housing body 15 includes a discharge port 21, which is in communication with the external refrigerant circuit. The second housing body 15 includes a communication passage 22, which allows communication between the discharge chamber 20 and the discharge port 21. During a compression operation of the motor-driven compressor, high-pressure refrigerant is discharged out of the compression mechanism 11 into the discharge chamber 20. Then, the high-pressure refrigerant flows through the communication passage 22, reaches the discharge port 21, and enters the external refrigerant circuit.

The compression mechanism 11 includes a fixed scroll 23, which is fixed to the inner side of the first housing body 14, and a movable scroll 24, which orbits with respect to the fixed scroll 23. Compression chambers 25 are defined between the fixed scroll 23 and the movable scroll 24. The refrigerant drawn from the suction port 19 into the first housing body 14 enters the compression chambers 25. The electric motor 12 is driven so that the movable scroll 24 orbits with respect to the fixed scroll 23. This changes the volumes of the compression chambers 25.

A support 26 is arranged between the electric motor 12 and the fixed scroll 23 in the first housing body 14. The support 26 forms part of the compression mechanism 11 and supports one end of a rotation shaft 27 of the electric motor 12. The other end of the rotation shaft 27 is supported by a bearing with respect to the end wall 18. The end wall 18 includes a flat outer surface 28, which extends in a direction orthogonal to the axis of the rotation shaft 27.

The electric motor 12 is driven by three-phase alternating-current power. The electric motor 12 includes a stator 29 and a rotor 30, which is fitted into the stator 29 and fixed to the rotation shaft 27. The stator 29 includes a stator core 31, which is fixed to an inner wall of the first housing body 14, and U-phase, V-phase, and W-phase stator coils 32, which are wound around the stator core 31. One end of a wire that forms the stator coil 32 of each phase is drawn from the stator coil 32 as a lead wire 33, which receives power that is supplied from a drive circuit unit 36 (described below).

A base 34 and a cover body 35 are arranged on the outer side of the housing 13. The base 34 is arranged on the outer surface 28 (surface opposite to the surface facing electric motor 12) of the end wall 18 of the first housing body 14. The cover body 35 is arranged on the base 34. The base 34 and the cover body 35 define an accommodation cavity 37, which accommodates the drive circuit unit 36 that drives the electric motor 12. The base 34 and the cover body 35 are fixed to the first housing body 14 by a bolt 38. The cover body 35, which covers the drive circuit unit 36, is formed from an aluminum metal material in the same manner as the first housing body 14. The drive circuit unit 36 is arranged on the outer surface 28 of the end wall 18 of the first housing body 14 and accommodated in the accommodation cavity 37. The drive circuit unit 36 includes a power module 39, which includes switching elements, other electronic components (only transformer 40 is shown in FIGS. 1 and 2), and a multi-layer board 41, on which electronic components are mounted. The power module 39 is supplied with power for driving the motor-driven compressor from the outside and converts the supplied direct-current power into alternating-current power.

The base 34 of the first embodiment is formed from an aluminum metal material having superior thermal conductance. The base 34 has the form of a plate and includes a first flat surface 42, which abuts against the outer surface 28 of the end wall 18, and a second flat surface 43, which is located at the side opposite to the first flat surface 42. Since the first flat surface 42 abuts against the end wall 18 of the first housing body 14, the base 34 is electrically connected to the first housing body 14, which is electrically grounded. The power module 39 is arranged on (in contact with) the second flat surface 43. This allows heat to be released from the base 34 to the end wall 18, the heat being generated during activation of power module 39. Legs 44 extend toward the multi-layer board 41 from the second flat surface 43 of the base 34. A threaded hole 46 is formed at the center of each leg 44. A bolt 45 is fastened to each threaded hole 46 to fix the multi-layer board 41 to the leg 44.

As shown in FIGS. 2 and 2A, the multi-layer board 41 of the first embodiment includes four-layer wiring layers 51 to 54. In the following description, the four-layer wiring layers 51 to 54 will be described as, in sequence from the one which is most distant from the base 34 to the one which is closest to the base 34: the first wiring layer 51, the second wiring layer 52, the third wiring layer 53, and the fourth wiring layer 54. Insulating layers 55 are arranged between the first wiring layer 51 and the second wiring layer 52, between the second wiring layer 52 and the third wiring layer 53, and between the third wiring layer 53 and the fourth wiring layer 54, respectively. The insulating layers 55 are formed by an insulator. The wiring layers 51 to 54 have conductive wiring patterns that are formed from copper foil. In the first embodiment, the first and fourth wiring layers 51 and 54 are used for communication, the second wiring layer 52 is used for power supply, and the third wiring layer 53 is used for ground. The second wiring layer 52 is electrically connected to the power module 39. The third wiring layer 53 of the first embodiment corresponds to a ground layer of the multi-layer board 41 and is electrically connected to the electrically-grounded first housing body 14 through the bolts 45 and the base 34.

As shown in FIG. 2, the transformer 40, which serves as an electronic component, is coupled to a surface of the fourth wiring layer 54 that is located at the side opposite to the third wiring layer 53. The transformer 40 of the first embodiment has the form of a cylindrical column. Electronic components other than the transformer 40 (not shown) are mounted on the surface of the first wiring layer 51 that is located at the side opposite to the second wiring layer 52 and on the surface of the fourth wiring layer 54 that is located at the side opposite to the third wiring layer 53. As shown in FIG. 2, the multi-layer board 41 includes through holes 56, which are formed at locations corresponding to the threaded holes 46 of the legs 44. The through holes 56 are aligned with the legs 44, and the bolts 45 are inserted through the through holes 56 and fastened to the threaded holes 46 of the legs 44 to fasten and fix the multi-layer board 41 to the legs 44. Each of the through holes 56 functions as a via (a via hole). The legs 44 and the third wiring layer 53 of the multi-layer board 41 are electrically connected through the bolts 45 that are inserted through the through holes 56.

A shield 57 extends from the second flat surface 43 toward the multi-layer board 41. As shown in FIGS. 1 and 2, the shield 57 has the form of a cylinder and substantially encompasses the entire transformer 40 except for the surface of the transformer 40 that is opposed to the multi-layer board 41. The shield 57 is electrically connected to the third wiring layer 53 by electrically connecting the legs 44 to the third wiring layer 53 of the multi-layer board 41. The shield 57, which encompasses the transformer 40, reduces leakage of noise radiated from the transformer 40 to the surroundings of the transformer 40. That is, by arranging the shield 57 on the base 34, the base 34 not only functions as a heat-releasing member that releases heat from the power module 39 but also functions to reduce leakage of noise radiated from the transformer 40.

An insulating gap G1 extends between the shield 57 and the circumferential surface of the transformer 40. An insulating gap G2 extends between the top of the transformer 40 and the base 34. In the first embodiment, a gap G3 extends between the end 58 of the shield 57 that is opposed to the multi-layer board 41 and the surface of the multi-layer board 41 (fourth wiring layer 54). This separates the shield 57 from the multi-layer board 41. The gap G3 allows for relative movement of the shield 57 and the multi-layer board 41. Thus, even when the motor-driven compressor vibrates, physical contact is avoided between the shield 57 and the multi-layer board 41.

The operation of the motor-driven compressor of the first embodiment will now be described. When power is supplied from the drive circuit unit 36 to the electric motor 12, the electric motor 12 is driven to activate the compression mechanism 11. As a result, the refrigerant drawn through the suction port 19 into the first housing body 14 enters the compression chambers 25. As the compression chambers 25 decrease in volume, the refrigerant in the compression chambers 25 is compressed and discharged to the discharge chamber 20.

When the motor-driven compressor is driven, the power module 39 performs a switching operation that generates heat. The heat generated by the power module 39 is released through the base 34 to the end wall 18 of the first housing body 14. In this manner, heat is released from the power module 39.

When the motor-driven compressor is driven, current fluctuation occurs in the drive circuit unit 36. This fluctuates the magnetic field intensity of the transformer 40 and generates noise. By transmitting the noise radiated from the transformer 40 to the first housing body 14, the shield 57 reduces leakage of the radiated noise to the surroundings of the transformer 40. The noise radiated from the transformer 40 toward the multi-layer board 41 is transmitted to the first housing body 14 through the third wiring layer 53 and the legs 44.

The shield 57 is separated from the multi-layer board 41. Thus, even if the motor-driven compressor vibrates when driven, the shield 57 and the multi-layer board 41 relatively move within the range of the gap G3 and thus do not physically contact each other. Further, since the shield 57 encompasses the transformer 40, the transformer 40 is protected from impacts applied from the outside.

The motor-driven compressor of the first embodiment has the advantages described below.

(1) The shield 57 projecting from the base 34 encompasses the transformer 40. Thus, most of the noise radiated from the transformer 40 is blocked by the shield 57 and transmitted to the grounded first housing body 14 through the base 34 that has the shield 57. This reduces leakage of the radiated noise to the surroundings of the transformer 40. Since leakage of the noise radiated from the transformer 40 is reduced, other wires and electronic components are less likely to receive the radiated noise.

(2) The legs 44 that fix the multi-layer board 41 to the first housing body 14 are electrically connected to the third wiring layer 53, which serves as a ground layer of the multi-layer board 41. Thus, the noise radiated from the transformer 40 toward the multi-layer board 41 is transmitted to the first housing body 14 through the third wiring layer 53 and the base 34, which has the legs 44.

(3) The shield 57 is separated from the multi-layer board 41. Thus, even when the motor-driven compressor vibrates, the shield 57 and the multi-layer board 41 relatively move within the range of the distance between the shield 57 and the multi-layer board 41 (gap G3). This avoids damage of the shield 57 and the multi-layer board 41 that would be caused by the vibration. Further, as compared to when the shield 57 is joined with the multi-layer board 41, the motor-driven compressor of the first embodiment does not require a means or operation for joining the shield 57 with the multi-layer board 41. This facilitates assembling of the motor-driven compressor.

(4) The shield 57 is located close to the transformer 40 within a range that ensures insulation of the shield 57 from the transformer 40. This allows heat to be released from the transformer 40 through the shield 57. As a result, the transformer 40 is easily cooled. This eases heat-withstanding conditions of the transformer 40 and allows the transformer 40 to be smaller than conventional transformers. Employing a compact transformer 40 reduces the size of the motor-driven compressor.

(5) The shield 57 encompasses the transformer 40. Thus, the transformer 40 is physically protected by the shield 57 and is less likely to receive physical damage. For example, even if the motor-driven compressor receives impact when hit, the shield 57 is first damaged. This reduces damage to the transformer 40.

Second Embodiment

A motor-driven compressor of a second embodiment will now be described. In the second embodiment, a shield is fixed to the multi-layer board. In the second embodiment, the same reference numerals are given to those components that are the same as the corresponding components of the first embodiment. Such components will not be described in detail.

As shown in FIGS. 3 and 3A, a base 64 and a shield 65 differ in form from the corresponding components of the first embodiment. More specifically, the shield 65 includes an upright portion 66 and a flange 61. The upright portion 66 projects from the second flat surface 43 of the base 64 toward the multi-layer board 41. The flange 61 extends from the end 67 of the upright portion 66, which is opposed to the multi-layer board 41, along the surface of the multi-layer board 41 (fourth wiring layer 54). The flange 61 includes threaded holes 62, and the multi-layer board 41 includes the through holes 56, which are arranged at locations corresponding to the threaded holes 62 of the flanges 61. Bolts 63 are inserted through the through holes 56 and fastened to the threaded holes 62 to join the shield 65 and the multi-layer board 41. Each of the through holes 56 functions as a via (a via hole) in the same manner as the first embodiment, and the bolts 63 electrically connect the shield 65 and the third wiring layer 53.

The second embodiment has advantages (1), (2), (4), and (5) of the first embodiment. Further, the flange 61 of the shield 65 increases the joining areas of the shield 65 and the multi-layer board 41. This reinforces the joining of the shield 65 and the multi-layer board 41 with the bolts 63. As a result, even when the motor-driven compressor vibrates, damage caused by the vibration is avoided in the shield 65 and the multi-layer board 41. The bolts 63 electrically connect the shield 65 and the third wiring layer 53, which serves as a ground layer of the multi-layer board 41. Thus, the noise radiated from the transformer 40 toward the multi-layer board 41 is easily transmitted to the electrically-grounded first housing body 14 through the third wiring layer 53 and the base 64, which has the shield 65.

Third Embodiment

A motor-driven compressor of a third embodiment will now be described. In the third embodiment, a shield is arranged on the end wall of the first housing body. In the third embodiment, the same reference numerals are given to those components that are the same as the corresponding components of the first embodiment. Such components will not be described in detail.

As shown in FIGS. 4 and 4A, a shield 72 is arranged on the end wall 18 of the first housing body 14 and extends from the outer surface 28 toward the multi-layer board 41. The shield 72 has the form of a cylinder and substantially encompasses the entire transformer 40 except for the surface of the transformer 40 that is opposed to the multi-layer board 41. The shield 72, which encompasses the transformer 40, blocks noise radiated from the transformer 40. That is, the function of reducing leakage of noise radiated from the transformer 40 is added to the first housing body 14. The base 74 does not have a shield and instead includes openings 71, through which the shield 72 is inserted. The base 74 and the first housing body 14 are electrically connected to each other. Thus, the shield 72 is electrically connected to the third wiring layer 53 through the bolts 45 and the base 74, which has the legs 44.

An insulating gap G1 extends between the shield 72 and the circumferential surface of the transformer 40. An insulating gap G2 extends between the top of the transformer 40 and the end wall 18. In the third embodiment, a gap G3 extends between the end 73 of the shield 72 that is opposed to the multi-layer board 41 and the surface of the multi-layer board 41 located at the side corresponding to the fourth wiring layer 54. This separates the shield 72 from the multi-layer board 41. The gap G3 allows for relative movement of the shield 72 and the multi-layer board 41. Thus, even when the motor-driven compressor vibrates, physical contact is avoided between the shield 72 and the multi-layer board 41.

In the third embodiment, the shield 72 projecting from the end wall 18 of the first housing body 14 encompasses the transformer 40. Thus, most of the noise radiated from the transformer 40 is transmitted to the first housing body 14, which has the shield 72. This reduces leakage of the radiated noise to the surroundings of the transformer 40. Further, the third embodiment has advantages (2) to (5) of the first embodiment.

Fourth Embodiment

A motor-driven compressor of a fourth embodiment will now be described. In the fourth embodiment, a shield is arranged on the cover body. In the fourth embodiment, the same reference numerals are given to those components that are the same as the corresponding components of the first embodiment. Such components will not be described in detail.

As shown in FIG. 5, the transformer 40 of the fourth embodiment is coupled to the surface of the multi-layer board 41 that is opposed to the cover body 35. A shield 81 extends from an inner surface of the cover body 35 (surface of cover body 35 opposed to multi-layer board 41) toward the multi-layer board 41. The shield 81 has the form of a cylinder and substantially encompasses the entire transformer 40 except for the surface of the transformer 40 that is opposed to the multi-layer board 41. The shield 81, which encompasses the transformer 40, blocks noise radiated from the transformer 40 and reduces leakage of the radiated noise to the surroundings of the transformer 40. That is, the function of reducing leakage of noise radiated from the transformer 40 is added to the cover body 35. The end of the shield 81 of the fourth embodiment is separated from the multi-layer board 41 in the same manner as the first embodiment. Further, since the base 34 and the first housing body 14 are electrically connected, the shield 81 is electrically connected to the third wiring layer 53 through the base 34 and the bolt 45.

In the fourth embodiment, the shield 81 projecting from the cover body 35 encompasses the transformer 40. Thus, most of the noise radiated from the transformer 40 is blocked by the shield 81 and transmitted to the electrically-grounded first housing body 14 through the base 34 and the cover body 35, which has the shield 81. This reduces leakage of the radiated noise to the surroundings of the transformer 40. Further, the fourth embodiment has advantages (2) to (5) of the first embodiment.

Fifth Embodiment

A motor-driven compressor of a fifth embodiment will now be described. In the fifth embodiment, a base having a shield is fixed to the cover body. In the fifth embodiment, the same reference numerals are given to those components that are the same as the corresponding components of the first embodiment. Such components will not be described in detail.

As shown in FIG. 6, the motor-driven compressor of the fifth embodiment includes a base 91, which serves as a heat-releasing member. The base 91 is arranged on the inner surface of the cover body 35 (surface of cover body 35 opposed to multi-layer board 41). The base 91 and the cover body 35 are fixed by bolts (not shown). The base 91 is formed from an aluminum metal material having superior thermal conductance in the same manner as the cover body 35. The base 91 has the form of a flat plate and includes a first flat surface 92, which abuts against the inner surface of the cover body 35, and a second flat surface 93, which is located at the side opposite to the first flat surface 92. The second flat surface 93 contacts the power module 39, which is electrically connected to the multi-layer board 41. Legs 94 extend toward the multi-layer board 41 from the second flat surface 93 of the base 91. A threaded hole 95 is arranged at the center of each leg 94. A bolt 45 is fastened to the threaded hole 95 to fix the multi-layer board 41 to the leg 94. The legs 94 are electrically connected to the third wiring layer 53 of the multi-layer board 41.

A shield 96 extends from the second flat surface 93 toward the multi-layer board 41. The shield 96 has the form of a cylinder and substantially encompasses the entire transformer 40 except for the surface of the transformer 40 that is opposed to the multi-layer board 41. Since the shield 96 is arranged on the base 91, the base 91 not only functions to release heat but also reduce leakage of noise radiated from the transformer 40.

An insulating gap G1 extends between the shield 96 and the circumferential surface of the transformer 40. An insulating gap G2 extends between the top of the transformer 40 and the base 91 (reference numerals G1 and G2 are omitted in FIG. 6). In the fifth embodiment, a gap G3 extends between the end 97 of the shield 96 that is opposed to the multi-layer board 41 and the surface of the multi-layer board 41 located at the side corresponding to the first wiring layer 51. This separates the shield 96 from the multi-layer board 41. The gap G3 allows for relative movement of the shield 96 and the multi-layer board 41. Thus, even when the motor-driven compressor vibrates, physical contact is avoided between the shield 96 and the multi-layer board 41.

In the fifth embodiment, the shield 96 projecting from the base 91 encompasses the transformer 40. Thus, most of the noise radiated from the transformer 40 is transmitted to the electrically-grounded first housing body 14 through the shield 96 and the base 91. This reduces leakage of the radiated noise to the surroundings of the transformer 40. Further, the fifth embodiment has advantages (2) to (5) of the first embodiment.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.

In the above embodiments, the drive circuit unit 36 is arranged on the outer surface of the end wall 18 of the first housing body 14. However, the drive circuit unit 36 does not have to be arranged on the outer surface of the end wall 18 of the first housing body 14. As long as the drive circuit unit is located outside the housing, the drive circuit unit may be arranged anywhere. For example, the drive circuit unit of the motor-driven compressor may be arranged on the outer surface of the cylindrical portion of the first housing body.

The motor-driven compressor of the third embodiment includes the base 74. However, as long as the shield 72 and the third wiring layer 53 are electrically connected, there is no need for the base 74. For example, the shield 72 may be electrically connected to the third wiring layer 53 by bolts.

The motor-driven compressor of the fourth embodiment includes the base 34. However, as long as the shield 81 and the third wiring layer 53 are electrically connected, the motor-driven compressor does not have to include the base 34. For example, the shield 81 may be electrically connected to the third wiring layer 53 by bolts.

In the above embodiments, the electronic component is a transformer. However, this is exemplary only. The electronic component may be a capacitor. In particular, the present invention is effective for electronic components that generate a large noise. Further, a plurality of electronic components may be shielded by a shield.

In the above embodiments, the shield is formed to be cylindrical in accordance with the column-shaped electronic component (transformer). However, the shield may have any shape as long as the shield covers the electronic component. For example, the shield may be polygonal.

In the above embodiments, a gap extends between the shield and the electronic component (transformer). However, this is exemplary only. For example, an insulating resin having superior thermal conductance may be molded around the electronic component so that the resin abuts against the shield. This allows heat to be easily transmitted from the electronic component to the shield through the resin. Thus, the release of heat from the electronic component is facilitated.

In the second embodiment, the shield is joined with the multi-layer board by bolts. However, this is exemplary only. The shield may be joined with the multi-layer board by, for example, an adhesive or solder. Alternatively, conductive grease may be filled between the shield and the multi-layer board.

In the third to fifth embodiments, the shield is separated from the multi-layer board. However, the shield does not have to be separated from the multi-layer board. For example, the shield may include a flange that is joined with the multi-layer board in the same manner as the second embodiment.

The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. 

1. A motor-driven compressor comprising: a compression mechanism that has a compression chamber and compresses refrigerant; an electric motor that drives the compression mechanism; a housing that accommodates the compression mechanism and the electric motor; a drive circuit unit that drives the electric motor, wherein the drive circuit unit includes a multi-layer board and electronic components mounted on the multi-layer board, and the multi-layer board includes a ground layer; a cover body that covers the drive circuit unit, wherein the cover body is arranged at an outer side of the housing; and a shield that encompasses at least some of the electronic components, wherein the shield is electrically connected to the ground layer of the multi-layer board.
 2. The motor-driven compressor according to claim 1, further comprising a heat-releasing member that contacts at least some of the electronic components, wherein the shield is located on the heat-releasing member.
 3. The motor-driven compressor according to claim 1, wherein the shield is located on the housing or the cover body.
 4. The motor-driven compressor according to claim 1, wherein the shield is separated from the multi-layer board.
 5. The motor-driven compressor according to claim 4, wherein the shield includes an end opposed to the multi-layer board, and a gap extends between the end and the multi-layer board.
 6. The motor-driven compressor according to claim 1, wherein the shield includes an end opposed to the multi-layer board, the end includes a flange that extends along a surface of the multi-layer board, and the flange is joined with the multi-layer board.
 7. The motor-driven compressor according to claim 1, further comprising a base that abuts against the housing or the cover body, wherein the base includes a leg to which the multi-layer board is fixed, and the base electrically connects the shield to the ground layer. 